Building structures constructed for human occupancy typically maintain the temperature and humidity conditions inside the building at a comfortable level for its occupants with the use of heating and air conditioning equipment controlled by a thermostat, whereas the temperature outside the building varies with atmospheric conditions. In a twenty-four hour day during most days of a year in most inhabited locations of the world, the temperature of a roof or an external wall that faces the sun typically ranges to levels below and above the desired indoor temperature which is in the mid seventies, Fahrenheit.
The roof or exterior wall structure of a typical modern building includes at least one layer of thermal insulation material which retards the transfer of heat between the inside and outside surfaces. If the insulation material present in the typical insulated wall or ceiling is sufficient, the transfer of heat during the high temperature portion of the day from the hot outside portion of the wall or ceiling to the lower constant inside temperate portion of the ceiling will be slow enough so that the temperature of the inside wall or ceiling may have no measurable increase in temperature. Later during the same day the exterior portion of the wall and ceiling will cool during the low temperature portions of the day, usually to a temperature that is lower than the inside temperature of the dwelling.
The rate at which heat will flow through a wall or ceiling into or out of a room maintained at a substantially constant temperature is dependent upon at least two factors: the difference between the temperature inside the room, across the ceiling and wall to the temperature outside the room, and the efficiency with which the ceiling or wall structure conducts heat between the inside temperate surfaces of the building and the hotter or cooler outside surfaces of the building. In order to reduce the rate of heat transfer across the ceiling or wall into or out of the building structure, a greater quantity of and a more efficient insulating material can be utilized. Such insulating materials can include, for example, fiberglass, mineral wool, urethane foams, cellulose and other materials well known in the art.
However, the cost of producing and installing the most efficient and most suitable insulating materials for a well-insulated ceiling or wall structure is rather high. Typically, the structure above the ceiling of a house includes a roof structure having several layers, such as an exterior layer of shingles and felt, several intermediate layers of wood boards, parallel joists, and wall board panels attached thereto and extending horizontally for forming a ceiling, and layers of insulation dispersed about the joists and panels. Similarly, the exterior wall structure of a building includes several layers such as an exterior layer of brick, wood or other siding, an inner layer of wall board, and an intermediate layer of insulation. Although providing the conventional insulating materials in an attic space or in the exterior walls of a building structure can be effective at reducing heat transfer through the walls or ceilings, etc., the insulation materials are expensive, are bulky to handle, difficult to install, and in some instances are not very effective. Also, some structures are not built with enough space to accommodate enough insulation to adequately insulate the structure.
It has been known in the past to use phase change materials to store heat by causing a change in the "state" or "phase" of the materials from a solid to a liquid. Generally, the heat applied to a phase change material is "consumed" by the material during its conversion from solid state to liquid state, while the phase change material maintains a substantially constant temperature. In reverse, the heat which was absorbed by the change to the liquid phase is released when the phase change material gives up its latent heat of liquification and turns into its solid state. Some examples of phase change materials for isothermally storing and releasing heat are paraffin, calcium chloride hexahydrate, sodium sulfate, and Glauber's salt.
An example of using phase change material as an insulator is found in U.S. Pat. No. 2,876,634 to Zimmerman et al. which shows a thermodynamic tea cup having an intermediate layer of phase change materials. The tea cup provides a means for effecting a rapid cooling of heated liquids to a satisfactory temperature for maintaining the contents of the cup at that temperature. Another U.S. Pat. No. 3,463,140 to Rollor, Jr. discloses a double walled container, defining an annulus. Paraffin is inserted in the annulus so that when a hot liquid is poured into the container, some of the heat from the liquid is transmitted to and stored in the paraffin as the paraffin fuses at a temperature which is approximately the optimum temperature for drinking hot liquids. Furthermore, U.S. Pat. No. 4,603,106 to Ryan illustrates another thermodynamic food and beverage container. The Ryan container includes a heat storage material disposed therein for regulating the temperature of the food and beverage within the container. Therefore, the prior art known to the inventor shows relatively small containers for containing and maintaining the temperature of a small quantity of material.
One of the main problems with using phase changing materials in a practical application for isothermally storing and releasing heat in a large structure such as a building is containing the quantity of phase change materials properly dispersed over a large area. Another problem with using phase changing materials in a practical application is containing the phase change material when in its liquid phase in an optimum position whereby it will perform its phase changing between its liquid and solid states continually and in an evenly distributed manner. Particularly, when the material liquifies, the liquid has an ability to move under the influence of gravity or to become absorbed into an adjacent material. If dislocated while in its liquid phase, the phase change material might be dislocated from its optimum position for its next phase change occasion. Also, if the phase change material is not retained in one position but is allowed to leak or move to other areas, the concentration of the phase change material in the water admixture is likely to change and is likely to cause a change in the performance of the phase change material.
Therefore, while the latent heat absorption and release capabilities of certain phase change materials have been known and used in limited ways in the past, no known practical and commercial use has been made of phase change materials in conjunction with insulation materials for insulating living spaces from one another, such as the ceiling area or exterior walls of a building structure from the atmosphere. It is to the provision of such a phase change insulation system that the present invention is primarily directed.